Monitoring PPP

You can monitor PPP activity with the show interface and debug ppp chap commands. The show interface command enables you to view PPP, LCP, and NCP information. The following output shows an example of PPP activity on an interface:

Notice that the "show interface" in the following example is abbreviated to "sh int". Almost all Cisco commands can be abbreviated. However, we recommend you use the full command until you are comfortable with all aspects of configuration. The abbreviations are hard to remember at first, but fairly easy to recognize once written. You will not be asked to provide any abbreviation on the test and you will probably not see any. However, we want to make sure you know they exist and will include some as we go along so you can see what they are like.

 RouterA#sh int s0 Serial0 is up, line protocol is up   Hardware is HD64570   Internet address is 172.16.1.1/16   MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,     rely 255/255, load 1/255   Encapsulation PPP, loopback not set, keepalive set (10 sec)   LCP Open   Open: IPCP, CDPCP   Last input 00:00:06, output 00:00:06, output hang never   Last clearing of "show interface" counters never   Input queue: 0/75/0 (size/max/drops); Total output drops: 0   Queueing strategy: weighted fair   Output queue: 0/1000/64/0 (size/max total/threshold/drops)      Conversations  0/2/256 (active/max active/max total)      Reserved Conversations 0/0 (allocated/max allocated)   5 minute input rate 0 bits/sec, 0 packets/sec   5 minute output rate 0 bits/sec, 0 packets/sec      34 packets input, 1303 bytes, 0 no buffer      Received 34 broadcasts, 0 runts, 0 giants, 0 throttles     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort      72 packets output, 2819 bytes, 0 underruns      0 output errors, 0 collisions, 14 interface resets      0 output buffer failures, 0 output buffers swapped out      41 carrier transitions      DCD=up  DSR=up  DTR=up  RTS=up  CTS=up RouterA# 

The debug ppp chap command displays the CHAP packet exchanges and PAP exchanges. The following output displays an example of the authentication handshake sequence:

 RouterA# debug ppp chap Serial0: Unable to authenticate. No name received from peer Serial0: Unable to validate CHAP response.          USERNAME pioneer not found. Serial0: Unable to validate CHAP response.          No password defined for USERNAME pioneer Serial0: Failed CHAP authentication with remote. Remote message is Unknown name Serial0: remote passed CHAP authentication. Serial0: Passed CHAP authentication with remote. Serial0: CHAP input code = 4 id = 3 len = 48 

The debug ppp chap command displays the reason why the CHAP request failed.

Once you have finished examining the debug output, use the no debug all command to turn off the debugging feature.